Along with continuous development of the semiconductor technology, semiconductor packages are required to not only have a compact size and a small profile but also have enlarged capacity for data storage. In light of increase in a load of data to be processed, relatively higher processing efficiency is achieved by processing data of the same size in a faster speed. The most direct way to enhance the processing speed of a semiconductor is to increase a frequency used by the semiconductor. However, in the case of a data transmission rate reaching a degree of Gb/s, several drawbacks are caused such as difficulty in efficiently dissipating heat, delay of signal time, electromagnetic interference, and so on, making fabrication of a semiconductor with higher performance become difficult. In particular for conventionally using copper circuits as data signal transmission media, conductivity of the copper circuits is hardly improved due to a limitation of the material characteristic thereof, such that the speed of signal transmission cannot be enhanced by a try to improve the conductivity.
For a structure using metal circuits to transmit signals, it is easily affected by interference from external noise or interference between internal circuits during a signal transmission process, thereby causing errors in signal transmission due to the interference. Accordingly, the structure for signal transmission should be provided with a suitable protective mechanism to prevent an influence from the interference on the signals especially in the case of high frequency transmission. However, such protective mechanism leads to considerable difficulty in a circuit design and requires an additional structural design, making the design and fabrication costs undesirably increased and thereby not effective to solve the problem in the current situation.
The conventional technology of signal transmission utilizes analog signal transmission by passing a current through an electrical conductor. However, the current signal processing method within circuits is mostly by digital processing, and signal conversion during the signal transmission process easily causes distortion and errors in data transmission after the signal conversion.
In order to overcome the drawbacks caused by the conventional analog signal transmission structure, a new technology is proposed to employ optical signals for transmission in place of electrical signals, which has a significant advantage that the optical signals are almost not interfered by electromagnetic waves, such that the quality of signal transmission is improved and distortion of signal transmission can be reduced. Further, it is not necessary to design a mechanism for preventing interference from the electromagnetic waves, thereby reducing the design and fabrication costs. As a result, the optical signal transmission technology becomes the mainstream of development.
The conventional optical signal transmission technology primarily uses a plurality of signal processing components such as optic fibers, an optic connector, an optical-to-electronic converter, an electronic-to-optical converter, and so on to perform digital data transmission. However, this technology is not favorable for the design of having a compact size and a small profile due to a requirement of high precision of optical alignment and a large system volume. Accordingly, it has been gradually evolved to design an opto-electric transmission system on a printed circuit board so as to improve the quality of transmission.
A conventional opto-electric transmission structure incorporated in a printed circuit board, as shown in FIG. 1A, comprises a waveguide 22 mounted on an upper surface of a carrier 21, wherein reflection surfaces 22a, 22b are respectively formed at two terminals of the waveguide 22 and positioned by an angle of 45 degrees relative to the upper surface of the carrier 21; a circuit board 23 mounted on the waveguide 22, and formed with two channels 231 at positions respectively above the reflection surfaces 22a, 22b at the two terminals of the waveguide 22; and an optical active component 24 and an optical receiving component 25 mounted on the two channels 231 of the circuit board 23 respectively.
Another conventional opto-electric transmission structure, as shown in FIG. 1B, comprises a waveguide 22 mounted on a carrier 21; two elevated circuit boards 23′ mounted on the carrier 21 and positioned above two terminals of the waveguide 22 respectively; and an optical active component 24 and an optical receiving component 25 attached to bottom surfaces of the circuit boards 23′ respectively, and located right above reflection surfaces 22a, 22b formed at the two terminals of the waveguide 22 respectively.
The optical active component 24 is for example a laser diode (LD), a light emitting diode (LED), or a vertical cavity surface emitting laser (VCSEL) diode. The optical passive component 25 is for example a photodiode (PD).
The structure of the waveguide 22 comprises a core layer 221 covered by a cladding layer 222, as shown in FIG. 2, wherein a refractive index (n1) of the core layer 221 is larger than a refractive index (n2) of the cladding layer 222, i.e. n1>n2. As shown in FIGS. 1A and 1B, when a photo beam from the optical active component 24 is emitted to the reflection surface 22a at one terminal of the waveguide 22, the reflection surface 22a allows the photo beam to be transmitted in the core layer 221 to the reflection surface 22b at the other terminal of the waveguide 22 by the total reflection principle, and the reflection surface 22b allows the photo beam to be reflected upwardly to the optical receiving component 25, such that optical transmission can be achieved by the waveguide 22 mounted on the carrier 21.
However, a drawback caused by the above conventional structure is that, it is difficult to form the pair of 45-degree reflection surfaces 22a, 22b at the two terminals of the waveguide 22. The above conventional structure also requires high precision of optical alignment and thus increases the fabrication costs thereof.
Further, since the photo beam must undergo two reflections via the reflection surfaces 22a, 22b, it may cause relatively greater loss of optical signals.
Referring to the conventional structure shown in FIG. 1A, as the optical active component 24 and the optical receiving component 25 are both mounted on one side of the circuit board 23, and the circuit board 23 must be formed with the two channels 231, this arrangement occupies a large area on the circuit board 23 and thus reduces a circuit layout area of the circuit board 23, such that the area of the circuit board 23 must be undesirably enlarged.
Referring to the conventional structure shown in FIG. 1B, the optical active component 24 and the optical receiving component 25 are attached to the elevated circuit boards 23′. However, this arrangement increases the overall thickness of the structure by using the elevated circuit boards 23′ and similarly leads to the area occupying drawback, such that the requirement of having a compact size and a small profile cannot be satisfied for the structure.
The optical active component 24 and the optical receiving component 25 also require high alignment precision (usually smaller than 20 μm) in emitting and receiving the photo beam, which is substantially equal to the precision required by a substrate for flip-chip connection. Thus, the assembly costs and difficulty in fabrication control of the structure are increased, thereby raising the fabrication costs.
Moreover, there is no heat dissipating structure provided for the optical active component 24 and the optical receiving component 25, such that the overall heat dissipating effect is not satisfactory, and the optical active component 24 and the optical receiving component 25 may easily be damaged by overheating.
Therefore, it is greatly desired to overcome the drawbacks caused by the foregoing conventional technology such as relatively greater loss of optical energy, occupation of substrate area, a complicated structure, high assembly costs, unsatisfactory heat dissipating performance, and so on.